Photo-electric modulating system



June 6, 1933. F. scHRGTER PHOTO-ELECTRIC MODULATING SYSTEM Filed NOV. 12, 1930 INVENTOR' m2 943mm ATTORNEY Tatented June 5, i933 UNETEE @TAT s rarest eerie raisin FRITZ SCHROTER, OF BERLIN, GERMANY, ASSIGNOR TO TELEFUNKEN GESELLSCHAIFT EfiR DRAHTLO$E TELEGBAPHIE M. B. 3., OF BERLIN, GERMANY, A CORPORATION E GEREEAHY EEO'I'O-ELECTRIC IflODULATING SYSTEIE Application filed November 12, 1930, Serial No. 495,060, and in Germany November 15, 1929.

The frequency band in electric television, as is well known, is so wide that carrier-frequency amplification is indispensable at least for pictures involving more than the average number of lines and average fineness. The rapid interruption of the scanning light employed in picture telegraphy for the production of such a carrier frequency by the aid of a perforated disk is mechanically impracticable because of the brief scanning time required for a picture element or unit. Periodic alteration of the intensity of the scanning light source itself has also not yet been realizable in practice. It has therefore been attempted by electrical ways and means to produce the carrier frequency by snperposing a radio frequency alternating current potential upon the direct current potential acting upon the photoelectric cell and then compensate for the wattless current flowing by virtue and by way of the electrode capacity by neutralizing circuit schemes.

This complication which is inconvenient in practice can be obviated according to the present invention by introducing in the c1r cuit of the photoelectric cell a radio frequency variable conduction resistance having the function of a pure interrupter rather than a radio frequency alternating current potential. To be sure, an attempt has pre viously been made, with the same end in View, to connect a second photoelectric cell in the circuit of the photoelectric cell subject to the action of the scanning light pencil, said second cell being struck by light subject to highfrequency interruptions with the result that its conducting power is periodically altered. However, the chief drawback of such scheme resides in the extremely high electric resistance of the interrupter photoelectric cell whereby the picture currents generated in the scanning cell are considerably weakened.

This disadvantage has been obviated by the arrangement hereinafter to be disclosed in more detail. The method consists in providing a Faraday cage in series with the scanning photoelectric cell in which, owing to the temporary entrance of the pendulous or 50 intermittent cathode-ray pencil of a sort of Braun tube, high-frequency conductivity the scanning photoelectric cell which in the analysis or exploration of the picture to be transmitted is struck by light in the direction of the arrow; numeral 2 denotes the suction or anode electrode of the cell 1; 3 is the lightresponsive electron-emissive electrode of cell 1; 4 is the anode or suction-current battery; 5 is the coupling resistance associating with amplifier tube 7 and 6 is a source of potential adapted to regulate. the grid biasing potential. Inside a Braun tube 10 is a. Faraday cage consisting of the screen electrode 8 having a hole, and of the plate 9 which is located at close proximity to the screen. The plate 9 is then connected with the suction or anode electrode 2 of the photoelectric cell 1. The parts of the cell 1 could also be constructionally united with the tube 10, for instance, in such a way that the emissive surface-3 exposed to the action of light is periodically struck directly by.

the electron pencil of the Braun tube. N umeral 12 represents the source for heating the cathode 11.

The electrons issuing from the hot cathode and accelerated from the potential source 14 pass through the anode 13 which in wellknown manner is shaped tubular. The cathode-ray pencil emerging therefrom passes through the electrostatic defiective field set up between the plates 15, though in lieu thereof also magnetic deflector coils could be employed. The cathode-ray pencil is subjected to spatial oscillations or pendulous motions by means of a radio frequency generator which charges the pair of plates 15 by way of a transformer 16, 17. As a result the said pencil is alternately caused to pass through the hole in the plate 8 and to be precluded from striking the interior of the Faraday cage by striking the side of the electrode 8. But every time that the cathode-ray pencil enters between electrode 8 and member 9, it produces high conductivity inside the cage which could be greatly assisted and enhanced by residual gases as Well as by secondary electron emission at the plate 9, with the result that the resistance which previously was practically 5 The plate 8 is grounded so that it will always be kept at ground potential.

Instead of resorting to spatial reci rocation of the electron pencil in the tu e 10,

periodic action upon the space between mem- 10 bers 8 and 9 can be effected also when the axis of the cathode-ray pencil is stationary by causing a radio frequency alternating current potential to act between anode 13 and the heated cathode 11 in lieu of a direct current potential. In that case the deflector device 15 is superfluous.

Having now described my invention, what I claim and desire to secure by Letters Patent is the following:

1. In combination, a translating element to convert energy of predetermined wavelengths supplied thereto into electric energy, an amplifier having one input terminal connected with one terminal of the translating element, a plurality of electrode elements normally electrically insulated one from the other, a connection between one electrode element and a second terminal of the translating element, and a connection between a second electrode element and a second input terminal of the amplifier, means for generating a cathode ray, means to reciprocate the generated ray across the electrode elements so as to introduce into the amplified output of the translating element an alternating current frequency which is-modulated by the energy supplied to the translating element, said alternating current varying in amplitude from minimum to maximum by the cathode ray establishing a path of zero conductive value between the electrode elements increasing in value progressively to a maximum upon the change in deflection of the ray from maximum to minimum deflection of the ray and from maximum to minimum amplitude in reverse order, said minimum deflection producing between the plurality of electrode elements a substantially direct conducting path both by virtue of the contact established between the electrode elements by the cathode ray and by the secondary emission efit'ects produced by the cathode ray upon at least one of the electrode elements.

2. In combination, a photoelectric cell for converting varying intensities of light and shadow into proportionate strength electric current impulses, a Faraday cage comprising a pair of electrodes located in close proximity, said cage having one element thereof connected with an electrode of said photoelectric cell, a cathode ray tube in cooperative arrangement with the Faraday cage, means associated with the cathode ray tube for deflecting the cathode ray generated therein for varying the conducting path between the electrodes thereof periodically between zero and a crest value by spatially reciprocating the cathode ray pencil of the said Braun tube across said Faraday cage for introducing into said photoelectric cell a chopper frequency superposed upon the direct currents produced by light striking the photoelectric cell:

3. In combination, a photoelectric cell having one'electrode thereof connected with the control electrode of a photo cell amplifier, a Faraday cage comprising a pair of electrodes located in close proximity, said cage having one element thereof connected with the second electrode of said photoelectric cell and a Braun tube arranged to project the controlled cathode ray pencil thereof towards said Faraday cage, and means cooperating with said Braun tube for spatially reciprocating said cathode ray pencil across said Faraday cage for varying the conducting power thereof between zero and a crest value so as to introduce into said photoelectric cell a chopper frequency to be superposed upon the direct currents produced by the action of light reaching the cell.

4. In combination, a photoelectric tube, an amplifier having one input terminal connecte ed with an electrode of said photoelectric tube for amplifying the output currents from said photoelectric tube, a plate-like electrode connected with one of the electrodes of said photoelectric tube. a second electrode provided with a central aperture and arranged in close proximity to said plate-like electrode, said apertured electrode being connected operatively with a second input terminal of said amplifier, a cathode ray device for normally projecting cathode rays toward the aperture of said apertured electrode, and means for alternately moving the said cathode ray into and out of said aperture so as tovary periodically between a zero and a crest value the conductin path between said two electrode elements or introducing into the amplified photoelectric tube output an alternating current frequency which is modulated directly by the photoelectric currents.

FRITZ soHRoTER. 

